An important neuropathological manifestation of Alzheimer's disease is the presence of amyloid depositions in brains and leptomeninges of afflicted individuals. However, amyloid depositions are not unique to Alzheimer's disease. They also occur in Down's syndrome and hereditary cerebral hemorrhage with amyloidosis of the Dutch type and to a lesser degree in the normal aging brain. A major component of the amyloid plaque is the amyloid beta protein. This peptide is derived from a much larger protein termed the amyloid beta precursor protein (APP) through abnormal proteolytic degradation. Several lines of evidence suggest that increased or altered APP gene expression is an essential factor in a multistep process leading to the formation of amyloid deposits. This emphasizes the importance of elucidating the mechanisms of APP gene regulation. A sequence element in the proximal promoter region of the APP gene was found to be essential for high levels of expression. This sequence element contains a binding domain for a novel nuclear binding factor. This novel trans-acting factor will be characterized and its gene cloned. The optimal conditions for factor binding will be determined. The factor will be purified by affinity chromatography and the subunit composition determined. The mode of action of the binding factor in transcriptional regulation will be analyzed by transient transfection, in vitro transcription and in vivo footprinting. The cDNAs of the subunits will be cloned and sequenced. This will yield information on mRNA structure and protein sequence. The gene(s) coding for the binding factor will be cloned. The exon/intron boundaries and the promoter region will be characterized. The chromosomal localization will be determined. These experiments will set the stage for future analysis of the regulation of the genes coding for the binding factor and their role in Alzheimer's disease and Down's syndrome.